The present invention relates to the preparation and use of rotating element sheet material including dual vector-field addressing components. More particularly, the present invention relates to the preparation and use of rotating element sheet material having both electric and magnetic addressing components.
Rotating element sheet material has been disclosed in U.S. Pat. Nos. 4,126,854 and 4,143,103, both hereinabove incorporated by reference, and generally comprises a substrate, an enabling fluid, and a class of rotatable elements. As discussed more below, rotating element sheet material has found a use as xe2x80x9creusable electric paper.xe2x80x9d FIGS. 1 and 2 depict an enlarged section of rotating element sheet material 50, including rotatable element 10, enabling fluid 20, cavity 30, and substrate 40. Observer 60 is also shown. Although FIG. 2 depicts a cylindrically shaped rotatable element and cavity, many other shapes will work and are consistent with the present invention. As disclosed in U.S. Pat. No. 5,389,945, herein incorporated by reference, the thickness of substrate 40 may be of the order of hundreds of microns, and the dimensions of rotatable element 10 and cavity 30 may be of the order of 10 to 100 microns.
In FIGS. 1 and 2, substrate 40 is an elastomer material, such as silicone rubber, that accommodates both enabling fluid 20 and the class of rotatable elements within a cavity or cavities disposed throughout substrate 40. The cavity or cavities contain both enabling fluid 20 and the class of rotatable elements such that rotatable element 10 is in contact with enabling fluid 20 and at least one translational degree of freedom of rotatable element 10 is restricted. The contact between enabling fluid 20 and rotatable element 10 breaks a symmetry of rotatable element 10 and allows rotatable element 10 to be addressed. The state of broken symmetry of rotatable element 10, or addressing polarity, can be the establishment of an electric dipole about an axis of rotation. For example, it is well known that small particles in a dielectric liquid acquire an electrical charge that is related to the Zeta potential of the surface coating. Thus, an electric dipole can be established on a rotatable element in a dielectric liquid by the suitable choice of coatings applied to opposing surfaces of the rotatable element about an axis of rotation.
The use of rotating element sheet material as xe2x80x9creusable electric paperxe2x80x9d is due to that fact that the rotatable elements are typically given a second broken symmetry, a multivalued aspect, correlated with the addressing polarity discussed above. That is, the above-mentioned coatings may be chosen so as to respond to incident electromagnetic energy in distinguishable ways, as indicated in FIG. 2, for example. Thus, an applied vector field can control the aspect of rotatable element 10 to favorably situated observer 60.
For example, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, rotatable element 10 may comprise a black polyethylene generally spherical body with titanium oxide sputtered on one hemisphere, where the titanium oxide provides a light-colored aspect in one orientation. Such a rotatable element in a transparent dielectric liquid will exhibit the desired addressing polarity as well as the desired aspect.
II.A. Rotatable Elements with Two-valued Aspects
A multivalued aspect in its simplest form is a two-valued aspect. When the aspect is the chromatic response to visible light, a rotatable element with a two-valued aspect can be referred to as a bichromal rotatable element. Such a rotatable element may be fabricated by the union of two layers of material as described in U.S. Pat. Nos. 5,262,098 and 6,147,791, herein incorporated by reference.
FIGS. 3-6 depict rotatable element 10 with a two-valued aspect and an exemplary system that use such rotatable elements from the prior art. In FIG. 3, rotatable element 10 is composed of first layer 70 and second layer 80 and is, by way of example again, a generally cylindrical body. The surface of first layer 70 has first coating 75 at a first Zeta potential, and the surface of second layer 80 has second coating 85 at a second Zeta potential. First coating 75 and second coating 85 are chosen such that, when in contact with a dielectric fluid (not shown), first coating 75 has a net negative electric charge with respect to second coating 85. This is depicted in FIG. 3 by the xe2x80x9cxe2x88x92xe2x80x9d and xe2x80x9c+xe2x80x9d symbols respectively. Furthermore, the combination of first coating 75 and the surface of first layer 70 is white-colored, and the combination of second coating 85 and the surface of second layer 80 is non-white-colored, indicated in FIG. 3 by hatching. One skilled in the art should appreciate that the material associated with first layer 70 and first coating 75 may be the same. Likewise, the material associated with second layer 80 and second coating 85 may be the same.
FIG. 4 depicts no-field set 110. No-field set 110 is a subset of randomly oriented rotatable elements in the vicinity of vector field 100 when vector field 100 has zero magnitude. Vector field 100 is an electric field. No-field set 110, thus, contains rotatable elements with arbitrary orientations with respect to each other. Therefore, observer 60 in the case of no-field set 110 registers views of the combination of second coating 85 and the surface of second layer 80, and first coating 75 and the surface of first layer 70 (as depicted in FIG. 3) in an unordered sequence. Infralayer 55 forms the backdrop of the resulting view. Infralayer 55 can consist of any type of material, including but not limited to other rotatable elements, or some material that presents a given aspect to observer 60.
FIGS. 5 and 6 depict first aspect set 120. First aspect set 120 is a subset of rotatable elements in the vicinity of vector field 100 when the magnitude of vector field 100 is nonzero and has the orientation indicated by arrow 105. In first aspect set 120, all of the rotatable elements orient themselves with respect to arrow 105 due to the electrostatic dipole present on each rotatable element 10. In contrast to no-field set 110, observer 60 in the case of first aspect set 120 registers a view of a set of rotatable elements ordered with the non-white-colored side up (the combination of second coating 85 and the surface of second layer 80 as depicted in FIG. 3). Again, infralayer 55 forms the backdrop of the resulting view. In FIGS. 5 and 6, rotatable element 10, under the influence of applied vector field 100, orients itself with respect to vector field 100 due to the electric charges present as a result of first coating 75 and second coating 85. FIG. 5 is a side view indicating the relative positions of observer 60, first aspect set 120, and infralayer 55. FIG. 6 is an alternate view of first aspect set 120 from a top perspective. In FIG. 6, the symbol ⊙ indicates an arrow directed out of the plane of the figure.
One skilled in the art should appreciate that first aspect set 120 will maintain its aspect after applied vector field 100 is removed, in part due to the energy associated with the attraction between rotatable element 10 and the substrate structure, as, for example, cavity walls (not shown). This energy contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 50, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, and discussed in more detail below.
Further still, one skilled in the art should appreciate that no-field set and first aspect set discussed above in FIGS. 4-6 can form the elements of a pixel, where vector field 100 can be manipulated on a pixel by pixel basis using an addressing scheme as discussed, for example, in U.S. Pat. No. 5,717,515, herein incorporated by reference.
For example, U.S. Pat. No. 4,126,854 entitled xe2x80x9cTwisting Ball Panel Displayxe2x80x9d issued Nov. 21, 1978, and U.S. Pat. No. 4,143,103 entitled xe2x80x9cMethod Of Making A Twisting Ball Display,xe2x80x9d issued Mar. 6, 1979, both by Sheridon, describe a rotating element sheet material that comprises bichromal rotatable elements contained in fluid-filled cavities and embedded in an elastomer medium. One segment of the bichromal rotatable elements has a larger electrical charge in contact with the fluid and in the presence of the electrical field than the other segment. Thus, for a given polarity of applied electrical field, one segment will rotate toward and be visible to an observer of the display. Applying the opposite polarity of electrical field will cause the rotatable element to rotate and present the other segment to be seen by the observer.
U.S. Pat. No. 4,143,103 describes the response of the bichromal rotatable element to the applied electrical field as a threshold response. That is, as the external field is increased, the bichromal rotatable element remains stationary in position until a threshold voltage is reached, at which time the rotatable element starts to rotate from its initial position. The amount of rotation increases with an increasing electrical field until a 180-degree rotation can be achieved. The value of the external field that causes a 180-degree rotation is called the full addressing voltage.
The response pattern of the bichromal rotatable element to an external electrical field determines the type of addressing that may be used to create images on the rotating element sheet material. There are known in the art three types of addressing schemes for displays. The first of these is active matrix addressing, which places the least demands on the properties of the display.
In active matrix addressing a separate addressing electrode is provided for each pixel of the display and each of these electrodes is continuously supplied with an addressing voltage. The complete set of voltages can be changed for each addressing frame. While this type of addressing places the least demands on the properties of the display medium, active matrix addressing is the most expensive, most complicated and least energy efficient type of addressing.
The second type of addressing scheme is passive matrix addressing. Passive matrix addressing makes use of two sets of electrodes, one on each side of the display medium. Typically, one of these consists of horizontal conductive lines and the other consists of vertical conductive lines. The conductive lines on the front surface or window of the display are necessarily aspect-transparent. To address the display medium a voltage is placed on a horizontal conductive line and a voltage is placed on a vertical conductive line. The segment of medium located at the intersection of these two lines experiences a voltage equal to the sum of these two voltages. If the voltages are equal, as they usually are, the sections of medium located adjacent to the each of the lines, but not at the intersection of the lines, experience xc2xd the voltage experienced by the section of medium at the line intersection. Passive addressing is less complicated and more energy efficient because the pixels of the display medium are addressed only for as long as is required to change their optical states. However, the requirements for a medium that can be addressed with a passive matrix display are significantly greater than for the active matrix case. The medium must respond fully to the full addressing voltage but it must not respond to xc2xd the full addressing voltage. This is called a threshold response behavior. The medium must also stay in whichever optical state it has been switched into by the addressing electrodes without the continuous application of voltagexe2x80x94that is, it should store the image without power. Passive addressing is the most widely used method of addressing displays and is the lowest cost.
The third type of addressing consists of a linear array of addressing electrodes in the form of a bar that can be moved over the surface of the sheet material. In this form of addressing, the sheet material is placed over or incorporates a grounding electrode and is protected from possible mechanical damage from the moving bar by placing a thin window between the bar and the rotating element sheet material. As the bar is moved over the sheet material, it applies voltages to specific pixels of the sheet material for short periods of time and generates a full image each time the bar is scanned over the surface. In one variation of this method, the addressing bar deposits image-wise charge on the surface of the window.
The requirements imposed on the sheet material by this form of addressing then depend on which type of addressing bar is used. If the addressing bar simply exposes the sheet material to voltages as it passes over the surface, then it is necessary for the rotating sheet material to exhibit threshold behavior. Thus the area of the sheet material directly under the addressing bar electrode must undergo a change in aspect when exposed to the full addressing voltage; but as the bar moves to the next row of pixels, this same area of sheet material must not respond to the diminished voltages experienced by the sheet material from the moving addressing bar. As in passive addressing, this requires that the sheet material have a sharp threshold response. This addressing bar also requires that the change in aspect occur completely during the time the addressing bar electrodes move over its vicinity, which usually limits the display frame addressing speed. U.S. patent application Ser. No. 09/037,767 by Howard et al. entitled xe2x80x9cCharge Retention Islands For Electric Paper And applications Thereofxe2x80x9d and also assigned to the same assignee as this application, describes an arrangement of addressing electrodes that greatly reduces the switching speed requirements of the medium due to this effect.
In U.S. patent application Ser. No. 09/037,767 the addressing bar deposits image-wise charge on or near the surface of the sheet material. The charge deposition addressing method relaxes the requirements on the sheet material. The addressing bar speed over the surface is limited only by the rate at which it can deposit image-wise charge, because the sheet material can respond to the voltage associated with the deposited charge pattern at its own speed. Threshold response behavior is not so important; however, the ability to store the image is because it can be expected that the image-wise charge deposited on the sheet material will leak off over a short period of time. However, addressing bars that can deposit image-wise charge on or near the sheet material tend to be bulky and more expensive than bars that simply impose image-wise voltages directly.
II.B. Rotatable Elements with Multivalued Aspect
A rotatable element with multivalued aspect may be generally fabricated as disclosed in U.S. Pat. No. 5,894,367, hereinabove incorporated by reference. An exemplary rotatable element 10 with multivalued aspect of the prior art is depicted in FIG. 7. Rotatable element 10 in FIGS. 7 and 8 is composed of core 140 within aspect-transparent cladding 137. Core 140 in FIGS. 7 and 8 is prism-shaped and is depicted as a square column. As used herein, the term xe2x80x9cprism-shapedxe2x80x9d refers to a polyhedron whose ends have substantially the same size and shape and are substantially parallel, and whose remaining sides are each substantially parallelograms. Depending upon the orientation of rotatable element 10 about an axis of rotation through core 140, rotatable element 10 may present first aspect surface 142, second aspect surface 144, third aspect surface 146, or fourth aspect surface 148 to a favorably situated observer. In FIG. 7, first aspect surface 142 and second aspect surface 144 are depicted from a view of one hemisphere of rotatable element 10, and in FIG. 8, third aspect surface 146 and fourth aspect surface 148 are depicted from a view of another hemisphere of rotatable element 10. In order to address rotatable element 10, the surface of aspect-transparent cladding 137 above first aspect surface 142 has first coating 130 at a first Zeta potential, and the surface of aspect-transparent cladding 137 above third aspect surface 146 has second coating 135 at a second Zeta potential such that first coating 130 has a net negative charge, xe2x80x9cxe2x88x92,xe2x80x9d with respect to second coating 135 when rotatable element 10 is in contact with a dielectric fluid (not shown). One skilled in the art should appreciate that rotatable element 10 may also be fabricated without aspect-transparent cladding 137. Accordingly, rotatable element 10 may simply comprise a substantially cylindrical core with a suitable choice of coatings or material in order to present four aspects to a favorably situated observer.
Another embodiment of a rotatable element with a multivalued aspect is depicted in FIGS. 9 and 10, and is composed of core 150 within aspect-transparent cladding 137. Core 150 in FIGS. 9 and 10 is prism-shaped and is depicted as a triangular column. Again, depending upon the orientation of rotatable element 10 about an axis of rotation through core 150, rotatable element 10 may present first aspect surface 152, second aspect surface 154, or third aspect surface 156 to a favorably situated observer. In FIG. 9, first aspect surface 152 and second aspect surface 154 are depicted from a view of one hemisphere of rotatable element 10, and in FIG. 10, third aspect surface 156 and first aspect surface 152 are depicted from a view of another hemisphere of rotatable element 10. In order to address rotatable element 10, the surface of aspect-transparent cladding 137 above first aspect surface 152 has first coating 130 at a first Zeta potential, and the surface of aspect-transparent cladding 137 above the apex where third aspect surface 156 and second aspect surface 154 meet has second coating 135 at a second Zeta potential such that first coating 130 has a net negative charge, xe2x80x9cxe2x88x92,xe2x80x9d with respect to second coating 135 when rotatable element 10 is in contact with a dielectric fluid (not shown). Again, one skilled in the art should appreciate that rotatable element 10 may be fabricated without aspect-transparent cladding 137. Accordingly, rotatable element 10 may simply comprise a substantially cylindrical core with a suitable choice of coatings or material in order to present three aspects to a favorably situated observer.
U.S. Pat. No. 5,894,367 describes the fabrication of rotatable element 10 from a macroscopic display element possessing scaled-up portions of material desired in the rotatable element. The macroscopic display element is then manipulated to form an extended filament so as to preserve the proportions of the component material. One skilled in the art should appreciate that this technique has been used in the production of optical fibers and channel electron multipliers.
Rotatable elements with multivalued aspect are generally utilized in rotating element sheet material that use canted vector fields for addressing. A canted vector field is a field whose orientation vector in the vicinity of a subset of rotatable elements can be set so as to point in any direction in three-dimensional space. U.S. Pat. No. 5,717,515, herein incorporated by reference, discloses the use of canted vector fields in order to address rotatable elements. The use of canted vector fields with rotating element sheet material 50 allows complete freedom in addressing the orientation of a subset of rotatable elements, where the rotatable elements have the addressing polarity discussed above. Exemplary systems utilizing rotatable elements with four-valued aspects and canted vector fields for addressing are depicted in FIGS. 11-17.
In FIG. 11, no-field set 160 depicts a subset of randomly oriented rotatable elements in the vicinity of vector field 100 when vector field 100 has zero magnitude. In no-field set 160, the rotatable elements have arbitrary orientations. Therefore, observer 60 in the case of no-field set 160 registers views of the combination of the surface of first aspect surface 142, second aspect surface 144, third aspect surface 146, and fourth aspect surface 148 in an unordered sequence. Again, infralayer 55 forms the backdrop of the aspect.
FIGS. 12 and 13 depict second aspect set 164 of the system introduced in FIG. 11. In second aspect set 164, observer 60 registers a coherent view of the combination of the second aspect surface 144. In second aspect set 164, all of the rotatable elements orient themselves such that first aspect surface 142 lies in the direction indicated by arrow 105, where arrow 105 indicates the direction of canted vector field 100. FIG. 12 is a side view indicating the relative positions of observer 60, second aspect set 164, and infralayer 55. FIG. 13 is an alternate view of second aspect set 164 from a top perspective.
Again, one skilled in the art should appreciate that fourth aspect set 168 will maintain its aspect after applied vector field 100 is removed due to the energy associated with the attraction between rotatable element 10 and the substrate structure, as, for example, cavity walls (not shown). This energy contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 50, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference.
Further still, one skilled in the art should appreciate that by suitable orientation of vector field 100, as indicted by arrow 105, any of the four aspects surfaces may be viewed by observer 60.
II.C. Rotatable Elements with Multivalued Aspect and Magnetic Latching
When utilizing rotatable elements with more than two aspects and a canted addressing vector field, it is desirable to ensure that an aspect that is addressed will be stable about an orientation that provides maximum viewing exposure for that aspect being viewed. One manner of accomplishing this is disclosed in U.S. Pat. No. 6,147,791 entitled xe2x80x9cGyricon displays utilizing rotating elements and magnetic latching,xe2x80x9d herein incorporated by reference. Multiaspect rotatable elements consistent with the invention disclosed in U.S. Pat. No. 6,147,791 are depicted in FIGS. 14 and 15. The rotatable elements of FIGS. 14 and 15 are similar to those depicted in FIGS. 7-10 and described above. The rotatable elements of FIGS. 14 and 15, however, also comprise rotatable latching components 170, preferably located at the apex or intersection of aspect surfaces. FIG. 14 depicts a rotatable element with four aspects and four rotatable latching components 170. FIG. 15 depicts a rotatable element with three aspects and three rotatable latching components 170. The rotatable latching components 170 contained within the rotatable elements preferably comprise hard magnetic material, as disclosed in U.S. Pat. No. 6,147,791, hereinabove incorporated by reference. xe2x80x9cHardxe2x80x9d magnetic materials are materials that exhibit some residual magnetism in the absence of an external field, such as ferromagnetic materials. Rotating element sheet material that provides maximum viewing exposure for an aspect being viewed and incorporating the rotatable elements of FIGS. 14 and 15 is depicted in FIGS. 16 and 17. FIG. 16 depicts rotating element sheet material 50 containing rotatable element 10 of FIG. 14 and includes sheet latching components 172. Similarly, FIG. 17 depicts rotating element sheet material 50 containing rotatable element 10 of FIG. 15 with sheet latching components 172. Sheet latching components 172 comprise soft magnetic material, or material that does not exhibit a significant amount of magnetization in the absence of an external field, such as paramagnetic or superparamagnetic materials. As depicted in FIGS. 16 and 17, the magnetic field that is present between rotatable latching components 170 and sheet latching components 172 will induce a torque about the axis of rotation of the rotatable element for any orientation other than the one that minimizes the distance between rotatable latching component 170 and sheet latching component 172.
One skilled in the art should also appreciate that rotatable latching components 170 and sheet latching components 172 will contribute to the xe2x80x9cwork functionxe2x80x9d associated with the attraction between rotatable element 10 and the substrate structure, as, for example, cavity walls (not shown), and that contribute to aspect stability. Again, this energy will contribute, in part, to the switching characteristics and the memory capability of rotating element sheet material 50, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference.
II.D. Parity Vector
One skilled in the art should appreciate that there is an additional parameter associated with multi aspect rotatable elements as depicted in FIGS. 7-17. Specifically, such multi aspect rotatable elements that utilize canted vector fields for addressing will exhibit a xe2x80x9cparity vector.xe2x80x9d The parity vector is a vector parallel to the axis of rotation of a multi aspect rotatable element and will have a direction associated with a specific ordering of multi aspect surfaces when proceeding in, for example, a clockwise rotation about the parity vector. Parity vector 270, in one embodiment, is depicted in FIGS. 18 and 19. For exemplary purposes only, rotatable element 10 in FIGS. 18 and 19 is configured such that first aspect surface 142 exhibits a red aspect, second aspect surface 144 exhibits a green aspect, third aspect surface 146 exhibits a blue aspect, and fourth aspect surface 140 exhibits a white aspect. This is depicted in FIGS. 18 and 19 by the use of the labels xe2x80x9cR,xe2x80x9d xe2x80x9cG,xe2x80x9d xe2x80x9cB,xe2x80x9d and xe2x80x9cKxe2x80x9d respectively. Parity vector 270 is parallel to the axis of rotation and is selected in FIGS. 18 and 19 to be in the same direction as a vector directed out of the axis of the rotatable element when a clockwise rotation (as indicated by arrow 271) produces the sequence xe2x80x9cR,xe2x80x9d xe2x80x9cK,xe2x80x9d xe2x80x9cB,xe2x80x9d xe2x80x9cG,xe2x80x9d xe2x80x9cR,xe2x80x9d etc. to favorably situated observer 60 (FIG. 18). Accordingly, parity vector 270 is parallel to the axis of rotation and is selected to be in the same direction as a vector directed into the axis of the rotatable element when a counterclockwise rotation (as indicated by arrow 273) produces the sequence xe2x80x9cR,xe2x80x9d xe2x80x9cK,xe2x80x9d xe2x80x9cB,xe2x80x9d xe2x80x9cG,xe2x80x9d xe2x80x9cR,xe2x80x9d etc. to favorably situated observer 60 (FIG. 19).
When addressing a plurality of multi aspect rotatable elements using a canted vector field, it is important that all of the rotatable elements in the rotating element sheet material exhibit a parity vector in the same direction. It is important due to the fact that a canted vector field directed to, for example, the right as in FIGS. 12 and 13 will cause the plurality of rotatable elements to exhibit the same aspect surface only if all of the parity vectors of the plurality of rotatable elements point in the same direction. One method of ensuring that a plurality of rotatable elements share the same parity vector is by magnetizing the rotatable element along the parity vector when it is manufactured, and prior to dispersing the plurality of rotatable elements to a plurality of cavities in the substrate. When the plurality of rotatable elements are dispersed in the substrate, as depicted in FIG. 20, the rotatable elements may be easily induced to self-align according to the magnetic polarity, and hence the parity vector. Accordingly, after the rotatable elements have been secured in the substrate and are ready to be addressed by an addressing vector field (as an electric field), they will exhibit the same direction for the plurality of parity vectors 270.
II.E. Work Function
As discussed above, a useful property of rotating element sheet material is the ability to maintain a given aspect after applied vector field 100 for addressing is removed. This ability contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 50, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference. This will be referred to as aspect stability. The mechanism for aspect stability in the above embodiments is generally the energy associated with the attraction between the rotatable elements and the containment structure, or xe2x80x9cwork function.xe2x80x9d A host of factors influence the magnitude of the energy associated with the work function including, but not limited to: surface tension of enabling fluid in contact with rotatable elements; the relative specific gravity of the rotatable elements to the enabling fluid; magnitude of charge on rotatable elements in contact with containment structure; relative electronic permittivity of enabling fluid and containment structure; xe2x80x9cstickinessxe2x80x9d of containment structure; and other residual fields that may be present. The applied vector field for addressing must be strong enough to overcome the work function in order to cause an orientation change; furthermore, the work function must be strong enough to maintain this aspect in the absence of an applied vector field for addressing.
FIG. 21 depicts an exemplary diagram of number 180, N, of rotatable elements that change orientation as a function of applied vector field 102, V of the prior art. The work function 184, VW, corresponds to the value of applied vector field 102 when the number 180 of rotatable elements that change orientation has reached the saturation level 186, Ns, corresponding to the orientation change of all rotatable elements 10.
II.F. Use of Magnetic Fields for Addressing
One manner of introducing a magnetic field to a region is depicted in FIG. 22. One skilled in the art should appreciate that a current 190, I, introduced to a current loop 194, will create a magnetic field. Exemplary flux lines 196 associated with the current 190 and current loop 194 are also depicted. Another manner of introducing a magnetic field to a region (not shown) is to introduce material to the region that exhibits inherent magnetization, such as a stylus composed of ferromagnetic material.
Again, in order to address rotatable elements with a vector field, the vector field must provide enough energy to overcome the work function. Conventionally, this energy has been provided by the interaction between a dipole and a vector field. One skilled in the art should appreciate that the energy U associated with the interaction of a dipole d in a vector field V may be expressed as a dot product between the dipole d and vector field V:
U=xe2x88x92dxc2x7V
Lee (L. L. Lee, xe2x80x9cA Magnetic Particles Display,xe2x80x9d IEEE Trans. On Elect. Devices, Vol. ED-22, Number 9, September 1975 and L. L. Lee, xe2x80x9cMatrix Addressed Magnetic Particles Display,xe2x80x9d in 1977 Soc. For Information Display International Symposium, Digest of Technical Papers, Boston, April 1977) has described the addressing of a twisting rotating element display in which the rotatable elements have a magnetic dipole with magnetic fields. U.S. Pat. No. 3,036,388 by Tate, and issued in May 1962 uses a stylus consisting of a magnetic dipole to address a display consisting of magnetized particles having black and white surfaces corresponding to a given magnetic polarity. More recently, U.S. Pat. No. 5,411,398 by Nakanishi et al. and entitled xe2x80x9cMagnetic Display Systemxe2x80x9d describes the use of a magnetic dipole to address a display consisting of black ferromagnetic particles and white, non-magnetic particles dispersed in an oil and in turn contained in microcapsules arranged in a layer. Upon application of a magnetic dipole, the black ferromagnetic particles are pushed to the rear of the microcapsules, revealing only the white particles, or pulled to the front of the microcapsules so that mostly only the black ferromagnetic particles can be seen by an observer.
It remains desirable, therefore, to utilize alternative forms of addressing rotating element sheet material in order to produce an aspect to a favorably situated observer.
In a first embodiment, the rotating element sheet material of the present invention comprises a plurality of rotatable elements disposed in a substrate and in contact with an enabling fluid, where at least one of the plurality of rotatable elements comprises: a core configured to present a first aspect in a first orientation and a second aspect in a second orientation, and where the first orientation and the second orientation are related by a rotational transformation about an axis of the rotatable element, and where the rotatable element in contact with the enabling fluid is further configured to exhibit a first addressing dipole configured to respond to a first vector field and a second addressing dipole configured to respond to a second vector field, and where the first addressing dipole and the second addressing dipole are configured such that the rotatable element exhibits the first aspect in the first vector field in a first direction and the second aspect in the second vector field in the first direction.
In a second embodiment, a system consistent with the present invention comprises the rotating element sheet material described above and an addressing system comprising an addressor; a first overlay, and a second overlay; where the addressing system introduces addressing vector fields capable of influencing the orientation of a subset of said plurality of rotatable elements due to the addressing dipoles of the rotatable elements.
In a third embodiment of the present invention, a method of addressing the rotating element sheet material described above comprises introducing a first vector field and a second vector field.